Exhaust reheat equipment for gasturbine engines



July 24, 1962 T. SEIFFERLEIN 3,

EXHAUST REHEAT EQUIPMENT FOR GASrTURBINE ENGINES Filed Feb. 21, 1955 United States Patent 3,045,425 EXHAUST REHEAT EQUIPMENT FOR GAS- TURBINE ENGINES Theo Seifferlein, Dammarie-les-Lys, France, assignor t0 Societe Nationale dEtude et de Construction dc Moteurs dAviation, Paris, France, a French company Filed Feb. 21, 1955, Ser. No. 489,446 Claims priority, application France Mar. 3, 1954 2 Claims. (Cl. Gil-35.6)

The present invention relates to an improvement in exhaust reheat devices for gas turbine engines, and more particularly in after-burning devices for turbo-jet units.

It is known that the temperature of the motive gases intended to drive a gas turbine should be limited in order to avoid damage to the turbine. On the other hand, it is also known that, at the outlet of the turbine, the temperature of the gases is substantially lower than at its inlet, as a result of the expansion to which these gases are subjected. It is however often necessary to have, at the outlet of a turbine, gases at high temperature which are intended to supply additional work which, for example, will enable the thrust to be increased in the case of a turbo-jet unit. To this end, devices are provided known as after-burning devices, that is to say devices which enable a combustion to be effected in the midst of the exhaust gases from the turbine with the object of increasing the temperature of these gases, which cannot, of course, run any risk of damaging the turbine, since the combustion takes place on the downstream side of this latter.

The known after-burning devices comprise injectors mounted in the exhaust conduit of the turbine, these injectors serving to introduce a supplementary quantity of fuel into the flow of exhaust gas which still contains a high proportion of combustion-supporting air.

As has already been stated, the temperature of the gases which is already restricted on the upstream side of the turbine, falls considerably as a result of the expansion which takes place in the turbine, to the point of making problematical the ignition of the supplementary fuel, and this ignition thus necessitates the use of special accessory devices of a more or less complex kind.

It has already been proposed to use ignition burners mounted in the combustion chamber which precedes the turbine and permitting of the introduction into this combustion chamber of a certain amount of fuel intended to produce an appreciable increase in the temperature of the gases on the upstream side of the turbine and especially a flame which, passing through the turbine, reaches the after-burning injectors and ensures by this means the ignition of the fuel discharged by these injectors. However, precautions must be taken so as to avoid an excessive increase in the temperature of the gases on the upstream side of the turbine and also to avoid an excessive duration of this operation, so that the flame which passes through the turbine is not too intense and does not have time to damage the turbine blades. It is especially necessary to adjust the supply of supplementary fuel to the combustion chamber in a very precise mnaner on the one hand, and strictly to limit the time of this injection of supplementary fuel on the other hand. This necessarily involves the use of delicate and complicated control devices, and creates a most unfortunate liability in that if, for any accidental reason, the ignition of the fuel discharged from the after burning injectors does not take place almost at once, it is impossible to prolong the action of the ignition burners without running the risk of irreparably damaging the turbine.

The present invention has for its object an after-burning device which enables the drawbacks referred to above to be overcome and which especially ensures the ignition of the supplementary fuel on the downstream side of the 3,645,425 Patented July 24, 1962 ICC turbine without subjecting the latter to an excessive temperature, even momentarily.

In accordance with the invention there is introduced in the midst of the hot driving gases on the upstream side of the turbine, a concentrated jet of fuel directed towards the turbine, the rotation of this latter serving to produce a sufficiently high degree of vaporisation of the fuel to enable it to be ignited, on the downstream side of the turbine, by the action of the hot gases which are discharged therefrom. This jet of fuel is preferably combined with an admission of cold air, which may be the secondary air under pressure delivered from the compressor which supplies the combustion chamber, this air being intended to prevent, at least in part, any direct contact between the fuel of the jet and the hot gases on the upstream side of the turbine. To this end, this air may be introduced through an orifice located in the vicinity of the fuel-injection member, and preferably surrounding the said member, so that the air forms a cold protective sheath around the jet by which it is entrained.

The output of fuel introduced in the form of a jet into the combustion chamber may be sufficient in itself to ensure the desired after-burning; in the contrary case, a supplementary quantity of fuel may be introduced on the downstream side of the turbine, in the zone in which is produced the flame due to the combustion of the firstmentioned fuel after its vaporisation by the turbine.

The description which follows below with regard to the attached drawings (which are given by way of example only and not in any sense by way of limitation) will make it quite clear how the invention may be carried into effect, the special features which may be brought out, either in the drawings or in the text, being understood to form a part of the said invention.

FIG. 1 is a schematic view in axial cross-section of a turbo-jet unit embodying an application of the improvement in accordance with the invention.

FIG. 2 is a partial view to a larger scale.

In the form of embodiment shown in the drawings, there can be seen at C the air compressor of the turbo-jet unit, at Ch, the combustion chambers, at T the gas turbine, and at R the reaction discharge nozzle provided with any known arrangement S for controlling the effective crosssection of its outlet orifice. The combustion chambers Ch are supplied with fuel by means of the burners B of standard type, whilst in the exhaust conduit of the turbine T, there is mounted an after-burning fuel injection system Pc cooperating with flameholding bafiles E for stabilising the flame.

The combustion chambers Ch have walls slightly spaced apart from those of the casing M of the engine, in known manner, so as to form a conduit A enabling the circulation of secondary cooling air around the combustion chambers Ch. Lateral openings 0 are formed in the walls of the combustion chambers so as to permit a part of this secondary air to pass into the interior of the chambers and thus to effect a dilution of the burnt gases before these gases pass into the turbine.

In conformity with the present invention, one or a number of injectors I is arranged in one or a number of combustion chambers Ch in the vicinity of the nozzle guidevanes D of the turbine T. This injector I is placed in one of the openings 0 and it is arranged in such manner as to produce a strongly concentrated jet J of fuel which is directed towards the nozzle guide-vanes D. This jet, by reason of its high velocity, entrains part of the secondary air which thus forms around it a kind of protective cold sheath which prevents direct contact of the fuel forming the jet I with the hot gases generated by the combustion chamber, and thus avoids any risk of general ignition of the fuel on the upstream side of the turbine T.

This jet, which passes through the guide-vanes D and the blades of the turbine, is subjected to a considerable turbulence which ensures intense atomisation and prevaporisation of the fuel, so that the latter when discharged from the turbine, is atomised and in intimate contact with the hot exhaust gases from the turbine in a zone at which the gases have still a fairly high temperature This intimate contact ensures the ignition of the fuel and there is formed a flame P which reaches the after-burning injectors Po and preferably, even as far as the flame-stabilising bafiles E. In its turn, this flame ensures infallibly the ignition of the fuel injected from P0.

It will be observed that, contrary to the known arrangements referred to above, the fuel discharged from the injector I does not burn in the combustion chamber Ch, and there is thus no increase in temperature on the upstream side of the turbine, and the injection period may be prolonged to any desired extent, and even for the whole period of operation of the after-burning system. Furthermore is not necessary to provide complicated devices for controlling the quantity of .fuel delivered, since the latter has simply to be sufficient for the flame F produced on the downstream side of the turbine to be long enough to reach the after-burning ring Pc and preferably the baffles E. This after-burning ring could even be dispensed with, the total quantity of supplementary fuel being then supplied by the injector or injectors I.

It will, of course, be understood that the application of the invention is not in any way limited to after-burning devices for turbo-jet units, but extends to any re-heating device for the gases on the downstream side of a turbine which makes use of a supplementary injection of fuel on the upstream side of the said turbine, in the form of a concentrated jet directed towards the turbine. In particular, the invention may find an interesting application in the case in which it is desired to effect re-heating of the driving gases between turbines in series flow arrangement, in certain gas-turbine installation.

It will also be clear that modifications may be made to the form of embodiment which has just been described,

and especially by the substitution of equivalent technical means, without thereby departing from the spirit or from the scope of the present invention.

What I claim is:

1. In a turbojet engine having a combustion space, a gas turbine and an exhaust-reheat tail pipe in series flow arrangement, an exhaust-reheat ignition device comprising a fuel injection nozzle designed to form a concentrated, solid jet of fuel and positioned at a peripheral point of said combustion space, said nozzle pointing towards said turbine, and a cool air supply leading to said peripheral point, around said nozzle, whereby said concentrated jet induces a sheath of cool air substantially surrounding said jet.

2. In a turbojet engine having an air compressor, a combustion chamber, a gas turbine, an exhaust-reheat tail pipe in series flow arrangement, and a flame-tube with a ported wall extending in said combustion chamber and dividing it into an inner flow path of primary combustion air and an outer flow path of secondary cool air, said paths communicating through the ports of said wall, an exhaust-reheat ignition device comprising a fuel injection nozzle designed to form a concentrated, solid jet of fuel and positioned at one of said ports, said nozzle pointing towards said turbine, whereby said concentrated jet induces a sheath of cool air substantially surrounding said jet.

References Cited in the file of this patent UNITED STATES PATENTS 2,502,332 McCollum Mar. 28, 1950 2,520,967 Schmitt Sept. 5, 1950 2,616,257 Mock Nov. 4, 1952 2,636,344 Heath Apr. 28, 1953 2,640,316 Neal June 2, 1953 2,651,178 Williams Sept. 8, 1953 2,715,311 Ooar Aug. 16, 1955 2,780,061 Clarke et a1. Feb. 5, 1957 2,780,915 Karen Feb. 12, 1957 

